1. Field of the Invention
The present invention is directed to a cellular hand held portable speakerphone system.
2. Description of Related Art
Cellular telephones are rapidly becoming commonplace. Indeed, in many fields a cellular telephone is almost a necessity. As cellular telephone technology advances, the size of cellular telephones is constantly shrinking to the point where cellular telephones can fit in the palm of the hand or a shirt pocket. There are, however, a number of problems associated with prior art cellular telephones.
For example, prior art cellular telephones which are designed for use outside the vehicle environment do not operate in a speakerphone mode. As such, the user's hands are not free during use. Moreover, standard telephones and vehicular cellular telephones which are designed to operate in a speakerphone mode suffer from a number of disadvantages. For example, acoustic coupling between the loudspeaker and the microphone causes a number of undesirable effects. Incoming speech at the speakerphone end is fed back from the loudspeaker to the microphone through an acoustic path and transmitted to the distant party with a delay. This is a form of "talker echo." Also, the distant party is subject to "listener echo." Another common speakerphone problem relates to the gain which is required in both the transmitting and receiving paths to make up for the loss introduced by moving the telephone away from the user's head. Signals from the microphone reach the loudspeaker via a sidetone path and come back to the microphone through the acoustic coupling described above, thus forming a loop. Too much gain in this loop causes "singing." One proposed solution to the "echo" and "singing" problems is a voice operated switching device which only allows one direction of transmission to be fully operative at a time. However, prior art switching devices detract from the naturalness of the conversation.
Another problem related to prior art cellular telephones is that they do not have recording capabilities. Thus, if the user is away from the cellular telephone when a call comes in, the calling party cannot leave a message.
Further problems are related to the fact that prior art cellular telephones are primarily designed to operate on battery power. When the battery is fully discharged in a prior art cellular telephone, the discharged battery must be removed and replaced with a charged spare battery. If a spare battery is unavailable, then the cellular telephone will be useless until the present battery has been re-charged.
Moreover, while many cellular telephones provide an indication of the battery charge state and/or level, it is difficult for the user of a cellular telephone to convert the indication of the state of the battery into meaningful information (e.g. such as whether the battery charge state is sufficient to allow the user of the telephone to make an additional cellular telephone call, to determine the length of the call that can be made, or to determine the amount of time remaining that the user can receive calls). If the battery level approaches full discharge while the cellular telephone is in use, then the user must alert the other party to this fact, hang up, replace the discharged battery with a spare (if available), and again call the other party. Such a procedure is extremely inconvenient.